Alkaline phosphatase and bone loading

The test measures the total activity of alkaline phosphatase in blood, reported in u/l. Phosphatase is an enzyme that splits phosphate groups off other molecules. Almost every tissue makes its own variant of it. The test sums those variants, drawing no distinction between them.

Two variants shape the picture in an adult athlete. The bone version arises in osteoblasts, the building cells of the skeleton. The liver version sits in the lining of the small bile ducts. A single result does not make that distinction.

The value therefore tracks the speed of bone turnover. That is useful to know, because bone turnover is rarely constant under heavy training.

The bands below come from NUMBER, the national project run by the NVKC. In men between 19 and 50 the band sits at 45 to 128 u/l. In women of the same age group it is 38 to 123 u/l. Your own laboratory report remains decisive.

Find the cause first, and only then a solution. With a raised alkaline phosphatase the first question is always the same. Did the rise come from bone, or from the bile ducts?

Gamma-GT decides that. The enzyme sits in the liver and bile ducts, and not in bone. If gamma-GT stays normal while this enzyme is raised, the rise almost certainly comes from bone tissue.

In a lifter there are then three candidates, in this order. A healing stress fracture, which lifts the value for weeks. A low vitamin D, which speeds up bone turnover without you noticing. And a long-standing low energy intake alongside a high training volume.

The vitamin D route deserves the most attention, because it is quiet and common. With a deficiency the building activity of osteoblasts increases. Calcium and phosphate belong in that conversation too, because those two help steer mineralisation.

If gamma-GT does rise alongside, the conversation turns to bile flow. Then also consider what you are taking. Anabolic steroids and some oral supplements load the liver, and drug-induced cholestasis is a real cause.

Almost every liver panel carries alkaline phosphatase as standard. Most lifters therefore meet the result without having asked for it.

Measuring it deliberately suits four situations. During recovery from a stress fracture, to follow the course.

With persistent bone or joint pain that does not fit a known injury. With a known or suspected vitamin D deficiency. And when using compounds that load the liver.

Never request the test on its own. Without gamma-GT beside it you cannot place a raised result, and the measurement is worth little.

Now the timing around training. For this enzyme a hard session matters little, because muscle tissue is not a source. If CK or AST run in the same draw, allow two days of rest first.

Fasting is generally unnecessary here. It is still cleaner. The intestinal form of this enzyme climbs after a fatty meal. People with blood groups O and B notice this most.